This is a single center prospective observational cohort study that aims to:

• examine and identify possible risk and susceptibility factors for the incidence and progression of chemotherapy-induced polyneuropathy (CIPN) in female patients primarily operated for early non-metastatic breast cancer who will receive adjuvant chemotherapy containing paclitaxel
• test different neurophysiological methods for early detection of CIPN
• explore changes that underlie the development of CIPN in relation to clinical presentations, neurophysiological assessment, including measures of small nerve fiber dysfunction, and possible biochemical, metabolic and genetic associations
• explore the effects of CIPN in the patient's lifestyle and quality of life for up to 12 months after the initiation of treatment

The patients who follow the inclusion criteria of the study will be asked to complete:

• a baseline evaluation prior to receiving treatment. This will include a bedside clinical-neurological evaluation, nerve conduction studies (NCS) and quantitative sensory tests of thermal threshold (QST), blood sampling, an oral glucose tolerance test, a skin biopsy, and answering of questionnaires for assessment of symptoms of peripheral neuropathy as well as self-reports on their pre-treatment health and lifestyle status and cancer specific symptomatology
• an on-treatment evaluation 4 weeks after the start of the treatment which will include NCS and QST
• a post-treatment evaluation 4 weeks after the end of treatment which will include the evaluations stated above. During this visit the participants will be provided with the REBECCA lifestyle monitoring system which will include a smartwatch, installation of a mobile app and a PC plugin. The patients will be also asked to fill in some self-rated evaluations as in the pre-treatment period. Researchers, based on the outcomes of the participants, will divide them in two study groups A. CIPN-group and B. No CIPN which will be monitored with the REBECCA monitoring system.
• a final evaluation. This will be performed 8 months after the post-treatment evaluation and it will include clinical-neurological evaluation, nerve conduction studies (NCS) and thermal threshold testing (QST). Additionally, the participants will be requested to fill in the same self-rated evaluations as in the baseline and the post-treatment.

Inclusion Criteria:

• Female patients
• Age of ≥ 18 years
• Newly operated primary breast cancer without metastatic disease receiving adjuvant chemotherapy containing paclitaxel
• No prior chemotherapy other than cyclophosphamide and epirubicin
• Eastern Cooperative Oncology Group (ECOG) performance status of 0-1
• Written informed consent
• Able to communicate with investigators, participate in testing and comply with the requirements of the study-protocol

Exclusion Criteria:

• Have received drugs suspected/known to cause peripheral neuropathy
• Have history of acquired or inherited neuropathy or other genetic disease with increased tendency to develop neuropathy
• Have known disturbed glucose metabolism, either diabetes mellitus or impaired glucose tolerance
• Have moderate to severe kidney, liver, lung or heart disease
• Have known symptomatic or other advanced spinal stenosis
• Have known autoimmune disease that potentially cause or contribute to neuropathy
• Have known HIV or active HBV or HCV infections
• Have known paraneoplastic syndrome
• Have known alcohol abuse
• Have known pregnancy or nursing

Patients will be identified as potential candidates and consecutively recruited from the oncology clinic at Karolinska University Hospital in Solna. Eligible candidates are patients who have been primarily operated for early non-metastatic breast cancer and are recommended by the multidisciplinary conference to receive adjuvant chemotherapy containing paclitaxel.